Which of the following statements does not differentiate between electrochemical cell and electrolyt — Electrochemistry Chemistry Question

💡 Solution & Explanation

Step 1 - Define Electrochemical and Electrolytic Cells To understand how to differentiate between the two classes of cells, let us first define their core operating principles: 1. **Electrochemical Cell (Galvanic/Voltaic Cell):** A device that converts chemical energy released from a spontaneous redox reaction into electrical energy. 2. **Electrolytic Cell:** A device that uses electrical energy from an external power source (such as a battery) to drive a non-spontaneous chemical reaction. Step 2 - Analyze Statement (A): Spontaneous or non-spontaneous nature of the chemical process * In an electrochemical cell, the overall chemical reaction occurs spontaneously on its own. The thermodynamic parameters are: $$\Delta G < 0 \quad \text{and} \quad E_{\ce{cell}} > 0$$ * In an electrolytic cell, the chemical reaction is non-spontaneous and requires external electrical work to proceed. The thermodynamic parameters are: $$\Delta G > 0 \quad \text{and} \quad E_{\ce{cell}} < 0$$ Therefore, the spontaneous or non-spontaneous nature of the chemical process **successfully differentiates** the two types of cells. Step 3 - Analyze Statement (B): Chemical reactions occurring at the electrodes The fundamental definition of electrodes in any chemical cell is based on the type of reaction that occurs on their surfaces, which remains invariant: * **Anode:** Regardless of the type of cell (electrochemical or electrolytic), the anode is always defined as the electrode where **oxidation** (loss of electrons) occurs: $$\ce{Red -> Ox + n e^-}$$ * **Cathode:** In both types of cells, the cathode is always defined as the electrode where **reduction** (gain of electrons) occurs: $$\ce{Ox + n e^- -> Red}$$ Since oxidation universally occurs at the anode and reduction universally occurs at the cathode in both cells, the basic chemical nature of the reactions at the electrodes **does not differentiate** between an electrochemical cell and an electrolytic cell. Step 4 - Analyze Statement (C): Positive and negative nature of anode The electrical sign (polarity) of the electrodes depends on the direction of electron flow and whether the cell is producing or consuming electrical energy: * **Electrochemical Cell:** * The anode is the site of spontaneous oxidation, releasing electrons onto the electrode. Thus, the anode is the **negative terminal ($-$)**. * The cathode is where cations are reduced by accepting electrons. Thus, the cathode is the **positive terminal ($+$)**. * **Electrolytic Cell:** * To force non-spontaneous oxidation, the anode must be connected to the positive terminal of an external power source. Thus, the anode is the **positive terminal ($+$)**. * The cathode is connected to the negative terminal of the external power source. Thus, the cathode is the **negative terminal ($-$)**. Therefore, the positive and negative nature of the anode **successfully differentiates** the two types of cells. Step 5 - Analyze Statement (D): EMF measurement * In an electrochemical cell, the electromotive force (EMF) is a positive value ($E_{\ce{cell}} > 0$) representing the electrical potential difference generated by the spontaneous cell reaction. This EMF can be directly measured using a voltmeter. * In an electrolytic cell, the cell itself does not generate a positive EMF. Instead, an external potential (voltage) must be applied to overcome the negative cell potential ($E_{\ce{cell}} < 0$, often called back-EMF) and the internal resistance of the cell. Therefore, the nature and measurement of EMF (generated potential vs. applied potential) **successfully differentiates** the two types of cells. Step 6 - Conclusion Since statement (B) describes a property (oxidation at the anode, reduction at the cathode) that is identical for both electrochemical and electrolytic cells, it does not differentiate between them. $$\text{Correct Option: } \boxed{\text{B}}$$